The peak expiratory flow (PEF) or peak expiratory flow rate (PEFR) is a measure of the maximum speed of expiration. It correlates with the degree of the obstruction in the airways allowing recognizing possible health problems before the actual symptoms. A peak flow meter is a medical instrument that measures the PEF and PEFR. It was introduced in 1950 by Basil Martin Wright, and since than it became a popular and easy-to-use technic to monitor patients with asthma and to optimize their treatment.

There is 235–330 million people suffering from asthma worldwide. This is a chronic disease that requires tight control with medication and self-monitoring. Beside from watching the signs and symptoms, including cough and wheeze, doctors advice their patients to perform PEF checks on regular basis and record the results.

The peak flow meter is a device that helps to control the asthma, reduce the number of exacerbations and safe life-threatening attacks.